Why Dubai was deluged

What caused the massive rains? Cloud seeding? Climate change? El Niño? The answers are trickling in.

Cars are stranded on a flooded street in Dubai following heavy rains on April 18, 2024. | Photo Credit: GIUSEPPE CACACE/AFP

Heavy rains and floods have been in the news in the hyper-arid West Asia region in recent years, including the flooding of Dubai and its airport. In 24 hours, on April 16, Dubai, United Arab Emirates, was inundated with rain that was more than a year’s quota for the city.

Average annual rainfall here is very low (50-150 mm) and much of it falls in short spells of intense rain. Flash floods in semi-arid and arid regions are not a new phenomenon but it seems to have become more frequent; and when it happens in a major city such as Dubai, which is a global air transportation hub, it catches the attention of many people.

So what caused the deluge? Cloud seeding? Climate change? El Niño? The answers are trickling in.

The World Weather Attribution group, comprising climate scientists, said in a statement: “While the researchers could not precisely determine how much of the increase [in rainfall] is due to human-caused climate change, they find that warming, caused by burning fossil fuels, is the most likely explanation for the increasing rainfall.”

That said, the heaviest showers occur in El Niño years, such as 2023-24. If twice the annual average rainfall falls in one or two days, it is definitely a major cause of floods especially in urbanised areas and arid and semi-arid ecosystems whose soils and very sparse vegetation have low ability to infiltrate and transpire.

Rain occurs when sufficient quantities of liquid water collect around particles in the atmosphere called cloud condensation nuclei (CCN) which are both anthropogenic in origin and natural (such as sea salt, sulphates from volcanic activity, volatile organic compounds released by forests, and emissions from plants) and become heavy enough to fall as rain droplets. The main point to remember is that CCN can become a trigger for rain to fall only if there is sufficient moisture for clouds to form in the first place.

A difficult estimation

Cloud seeding, a way to modify local weather in a limited area by inducing rain through artificial seeding of clouds with CNN particles, such as silver iodide, has been used for many decades across several places, including Dubai.

It is difficult to estimate exactly how much extra rain occurred because of cloud seeding over what may have occurred naturally, but some approximate estimates are now available. No two clouds are similar: they differ in moisture levels. So it is only over a longer period of time that evidence from unseeded and seeded conditions can be compared to make some estimates.

Vehicles are stranded in flood waters along a highway in Dubai. | Photo Credit: GIUSEPPE CACACE

Studies from around the world, including India, suggest a 5-30 per cent increase but the area impacted is generally small and costs are high. Furthermore, it should be noted that cloud seeding only triggers the existing moisture in the atmosphere to fall as a bit of additional rain and this could be at the cost of downwind regions. And so yes, in some storms, cloud seeding did make a measurable difference but not in the case of the recent deluge.

Although cloud seeding has been experimented with in this region, many extreme rain events, including some of the recent ones, have not been triggered by it. In any case cloud seeding has no influence on the amount of atmospheric moisture available, which was the main driver of the magnitude of the precipitation event.

In the future, as climate changes, there could be more precipitable moisture in some parts of the world, and cloud seeding at best could be a very local intervention, subject to an evaluation of its costs and benefits.

We are currently at about 1.2°C above pre-industrial global temperature. Global warming increases the rate of evaporation and evapotranspiration from regions that have high levels of moisture on both land and oceans. In addition, a warming atmosphere can hold 7 per cent more moisture with every degree Celsius increase.

However, climate models sometimes are unable to reproduce the observed past in terms of precipitation and so there is often a lot of uncertainty about future predictions. The latest IPCC AR6 assessment states that there is “medium confidence” that heavy precipitation would be detectably larger in the Arabian Peninsula at about 1.5°C of global warming compared to pre-industrial climate conditions, which is close to the current level of global warming.

Across countries in this region, low lying, flood-prone areas, a high degree of surfaces with limited permeability and moisture storage capacity from urban modification of land surfaces, inadequate drainage, the hyper-arid soils and sparse vegetation considerably increase the risk and severity of flash floods. Sometimes such events happen after a few decades during which a false sense of complacency about the safety of infrastructures and settlements sets in. Now there have been quite a few wake-up calls after devastating floods, tragic deaths and enormous property damage around the world.

Jagdish Krishnaswamy, an ecohydrologist and landscape ecologist, is the Dean of the School of Environment and Sustainability, Indian Institute for Human Settlements, Bengaluru.